1. Field of the Invention
The present invention relates to a workpiece transfer device for machine tools. The device is constructed so that a support member having a workpiece holding mechanism is mounted on a frame member and is extendable between a workpiece machining position and a workpiece loading/unloading position via a linear guide. The support member is moved in a reciprocating motion by a rack-and-pinion drive mechanism.
2. Discussion of the Related Art
In recent years, some machine tools are equipped with a workpiece transfer device that is designed to automatically and continuously perform such working processes as receiving an unprocessed workpiece from the workpiece stocker disposed at the workpiece loading/unloading position, loading the workpiece in a chuck of a spindle (which is at the workpiece machining position), receiving the processed workpiece from the chuck of the spindle, and unloading the workpiece at the workpiece stocker.
FIG. 8 shows a workpiece transfer device that has conventionally been provided. This device comprises a rectangular frame member 50 extending from a workpiece machining position to a workpiece loading/unloading position. The device also includes a support member 53 which is reciprocatably supported by two linear guides 51, 52 disposed on a top wall 50a and a side wall 50b of the frame member 50 and has a workpiece holding mechanism (not shown) mounted thereon. The device also includes a rack 54 disposed on the top wall 50a of the frame member 50 so as to extend along the linear guide 51. The device also includes a drive motor 56 for rotationally driving a pinion gear 55 engaged with the rack 54 to thereby move the support member 53 in a reciprocating fashion.
In this prior-art transfer device, the transfer device adopts a structure that the support member 53 is supported by two costly linear guides 51, 52. This causes a problem in that the cost for the whole device increases. Also, since the linear guides are disposed on two adjacent wall surfaces of the frame member, there is a need for ensuring the relative dimensional accuracy of the linear-guide fitting surfaces with the frame member surfaces. This accuracy also increases the cost of the transfer device.
Meanwhile, there is also a structure that allows the two linear guides to be reduced so that only one linear guide is used. In the transfer device shown in FIG. 7, one linear guide 61 is disposed on a top wall surface 60a of a frame member 60. A rack 64 is disposed on a bottom wall surface 60b on the symmetrically opposite side from the top wall surface 60a. The rack 64 has its right and left side faces pinched and held by a pair of cam followers 67. Also, a drive motor 66 rotationally drives a pinion gear 65 engaged with the rack 64.
In this structure, since one linear guide 61 can be used, cost increases can be reduced compared with the structure where two linear guides are used for support.
In this connection, general structural purpose steel tubes that have a relatively lower dimensional accuracy are adopted for the frame member 60. When using a structure where the linear guide 61 is fit on the top wall surface 60a of the frame member 60 and the rack 64 is disposed on the bottom wall surface 60b, there is difficulty in adjusting the vertical position of the rack 64 relative to the linear guide 61. If the vertical position is not properly adjusted then vibrations and/or noise can occur. Performing a machining process on the wall surfaces of the frame member 60 could solve the above problem; however, doing so would lead to impractical increases in cost.